Data Reduction

The majority of the data available to download from this website has been pre-processed by 'tracking' and 'mapping'. The small regions of the Sun used in helioseismology are generally observed for some period of time and it is necessary to track the one region in a frame co-rotating with the Sun. The observations of the spherical Sun are then mapped onto a plane projection. Here you can learn how the pre-processing is carried out and the reasoning behind it.

Tracking : Instructions to track the data.

Mapping : Information about different mappings.

Calculating L0, B0: To calculate the central latitude and longitude of disk centre as viewed by SOHO-MDI using soho_ephem.c (R. Bogart).

Solar coordinate definitions from NSO/GONG.

Some data reduction is done onsite/onboard, before it is made available for scientific use. Most of these details are covered in the Technical Papers given below.

Technical Papers

GONG merging: C. Toner. A paper on merging GONG data from different sites. GONG data is collected from various sites around the world, designed to obtain continuous observation of the Sun. The data from the different sites then needs to be 'merged' (description provided in the paper and also here).

GONG++ data reduction: F. Hill et al. A paper outlining the data reduction pipeline of GONG++ data.

GONG++ Pipeline map: Schematic of Local helioseismology pipeline.

MDI: Scherrer et al. MDI Team.The paper containing details of the Michelson-Doppler Interferomoter instrument.

MDI Performance characteristics: Zayer et al. A paper detailing some results and quality of performance of MDI.

MDI calibrations: From the MDI website, discusses plate scale, focus, jitter and tuning.

Image quality: From the MDI website, discusses factors which determine the quality of the image.

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